A leading international aid agency has issued a stinging attack on the United Nations mission in South Sudan, accusing it of a "shameful attitude" and leaving thousands of displaced people living in squalor.

Medecins Sans Frontieres (Doctors Without Borders, MSF) said on Wednesday that UN officials had left terrified civilians sheltering in a flood-prone part of a UN base "exposed to waterborne diseases and potential epidemics", even while acknowledging the camp was a "death trap".

"In a shocking display of indifference, senior United Nations Mission in South Sudan (UNMISS) officials have refused to improve living conditions for 21,000 displaced people," MSF said.

"The UNMISS decision not to improve conditions in Tomping is shameful," added MSF's emergency coordinator Carolina Lopez, referring to the UN base in South Sudan's capital Juba were thousands have sought refuge from a wave of ethnic violence.

"If nothing is done right now, the consequences, already horrific, could become fatal," she said, as the onset of the rainy season has seen bases flooded, latrines collapse and appalling public health conditions.

The fierce criticism came just days after UN Secretary-General Ban Ki-moon praised operations in South Sudan as an example of how lessons had been learned after the genocide in Rwanda.

But the UN on Wednesday rejected the criticisms of its mission in South Sudan.

"We are doing our best to decongest the site and encourage people to move voluntarily to better sites with better sanitation," UN spokesman Stephane Dujarric said.

"It is a huge logistical challenge to take care of these thousands of people."

'Aware of risks'

Nick Birnback, spokesman for the UN Department of Peacekeeping Operations, also rejected the MSF criticisms of UN officials in South Sudan.

"I strongly disagree with the assertions made by MSF against UNMISS and these views are not necessarily shared by the rest of the humanitarian community," Birnback said.

The UN was aware of the risks of epidemics and overcrowding, he added.

"De-congestion of overpopulated sites and cleaning up of areas posing an epidemic risk are essential and remain the basis of all efforts UNMISS is undertaking," he added.

Around 1,500 civilians had moved voluntarily from the area of the Tomping base in Juba posing the greatest of health risks.

PHOTO CAPTION

A displaced South Sudanese youth prepares food in the UN Mission in South Sudan (UNMISS) compound in Rumbek, March 19, 2014.

Al-Jazeera